You can use one of the NOISE generators in the Signal Processing tools, then direct it to one of the analog outputs of your DAQ card. You can then physically wire that output, through a high value of resistance, to your analog input. (This should be on the order of tens of megohms. You will have to experiment with the exact values:)
Eric
Eric P. Nichols
P.O. Box 56235
North Pole, AK 99705